Fix #15148. Capitalize PATH, hopefully leading to less confusion

Lib/shutil.py

@@ -972,7 +972,7 @@ def get_terminal_size(fallback=(80, 24)):
     return os.terminal_size((columns, lines))
 
 def which(cmd, mode=os.F_OK | os.X_OK, path=None):
-    """Given a command, mode, and a path string, return the path which
+    """Given a command, mode, and a PATH string, return the path which
     conforms to the given mode on the PATH, or None if there is no such file.
     `mode` defaults to os.F_OK | os.X_OK. `path` defaults to the result of
     os.environ.get("PATH"), or can be overridden with a custom search path."""